Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Annular brush seals have been proposed for use between a rotor and a surrounding casing in gas and steam turbines. The annular brush seal includes an annular backing plate and also includes bristles which are canted at typically a forty-five degree angle with respect to a radius line. A gas or steam turbine brush seal is made up of circumferentially-arrayed brush seal segments. Radial contact of the bristles with the rotor during turbine startup or shutdown causes unwanted wear and/or damage of the bristle free ends and also causes unwanted perturbations in the rotor itself.
It is known to position variable-clearance labyrinth-seal segments in a circumferential array between the rotor of the turbine and the circumferentially surrounding casing to minimize steam-path leakage. The ends of coil springs engage circumferentially-opposing and generally-matching holes in circumferentially-adjacent seal segments. The coil springs circumferentially urge apart circumferentially-adjacent seal segments. Such circumferentially-urging-apart causes the seal segments to move radially outward within a channel in the casing. This prevents damage to the labyrinth-seal teeth from transient radial movement of the rotor during turbine startup or shutdown. As the rotor reaches steady-state operating conditions, steam pressure builds up in the turbine, and such pressurized fluid enters the channel and pushes the seal segments radially inward such that the labyrinth-seal teeth are in close proximity to the rotor for more efficient sealing. Designs have been proposed which add brush-seal bristles to a labyrinth seal segment.